Pictures: U.S. Senate race -- who's in, who's out, who's a maybe

Murphy, who is serving his second term in the House, became the first major party candidate for Florida’s U.S. Senate seat in the 2016 election.

He has demonstrated appeal to Republicans, winning two elections to Congress in a district that supported Mitt Romney over Barack Obama.

After narrowly defeating then-U.S. Rep. Allen West, the controversial tea party Republican, in 2012, Murphy set out to avoid anything that could make him seem like a liberal Democrat. He repeatedly broke from his party and from President Obama — so much so that he was one of only four Democrats endorsed in 2014 by the U.S. Chamber of Commerce, which generally supports Republicans.

He continued to avoid being pigeonholed at the beginning of his second term, voting against most Democrats by supporting the Republican legislation to push through the controversial Keystone XL pipeline.

He won re-election with 60 percent of the vote in 2014 in a district that has more Republicans than Democrats in a year in which Republicans wiped out Democrats across the country.

Top Florida and national Democratic leaders are supporting Murphy for the nomination. But Democrats from the party's liberal wing believe he is too much like a Republican to energize the Democratic base if he wins the nomination. They argue that if Murphy is the party's candidate in November 2016, he'd end up losing -- just the way Republican-turned-independent-turned Democrat Charlie Crist lost the governor's race last year.

Above, President Barack Obama is greeted on the tarmac by Murphy, center, and Fort Pierce Mayor Linda Hudson, upon his arrival on Air Force One at St. Lucie International Airport, Saturday, March 28, 2015, in Fort Pierce.

Murphy, who is serving his second term in the House, became the first major party candidate for Florida’s U.S. Senate seat in the 2016 election.

He has demonstrated appeal to Republicans, winning two elections to Congress in a district that supported Mitt Romney over Barack Obama.

After narrowly defeating then-U.S. Rep. Allen West, the controversial tea party Republican, in 2012, Murphy set out to avoid anything that could make him seem like a liberal Democrat. He repeatedly broke from his party and from President Obama — so much so that he was one of only four Democrats endorsed in 2014 by the U.S. Chamber of Commerce, which generally supports Republicans.

He continued to avoid being pigeonholed at the beginning of his second term, voting against most Democrats by supporting the Republican legislation to push through the controversial Keystone XL pipeline.

He won re-election with 60 percent of the vote in 2014 in a district that has more Republicans than Democrats in a year in which Republicans wiped out Democrats across the country.

Top Florida and national Democratic leaders are supporting Murphy for the nomination. But Democrats from the party's liberal wing believe he is too much like a Republican to energize the Democratic base if he wins the nomination. They argue that if Murphy is the party's candidate in November 2016, he'd end up losing -- just the way Republican-turned-independent-turned Democrat Charlie Crist lost the governor's race last year.

Above, President Barack Obama is greeted on the tarmac by Murphy, center, and Fort Pierce Mayor Linda Hudson, upon his arrival on Air Force One at St. Lucie International Airport, Saturday, March 28, 2015, in Fort Pierce.

Lopez-Cantera comes out of Republican politics in Miami-Dade, the state’s largest county, where he was the elected property appraiser when Gov. Rick Scott picked him to replace the previous lieutenant governor who resigned under pressure from Scott.

Lopez-Cantera spent eight years in the Florida House, where he rose to the job of majority leader from 2010 to 2012.

Lopez-Cantera had one of the most grueling jobs in politics last year, campaigning around the state for his boss' re-election, which also gave him a full term as the state's No. 2.

He has a range of options, including staying put and seeking another state office in 2018 when all the other statewide elected officials will be term limited.

"I think we have enough Washington in Washington and I think maybe we need a little more Florida and this recipe that's worked for Florida in Washington," Lopez-Cantera said in an interview after he announced his intention to seek the Republican Senate nomination on July 15, 2015.

Former Palm Beach County Republican Chairman Sid Dinerstein sees him as a strong candidate. "He'll be a great person for the party. He's been throughout the state," Dinerstein said. "He has an infrastructure of contacts and fundraisers throughout the state."

Above, Lopez-Cantera greets supporters after announcing his candidacy for the Republican nomination for U.S. Senate in northwest Miami-Dade County on July 15, 2015.

Lt. Gov. Carlos Lopez-Cantera, Republican.

Lopez-Cantera comes out of Republican politics in Miami-Dade, the state’s largest county, where he was the elected property appraiser when Gov. Rick Scott picked him to replace the previous lieutenant governor who resigned under pressure from Scott.

Lopez-Cantera spent eight years in the Florida House, where he rose to the job of majority leader from 2010 to 2012.

Lopez-Cantera had one of the most grueling jobs in politics last year, campaigning around the state for his boss' re-election, which also gave him a full term as the state's No. 2.

He has a range of options, including staying put and seeking another state office in 2018 when all the other statewide elected officials will be term limited.

"I think we have enough Washington in Washington and I think maybe we need a little more Florida and this recipe that's worked for Florida in Washington," Lopez-Cantera said in an interview after he announced his intention to seek the Republican Senate nomination on July 15, 2015.

Former Palm Beach County Republican Chairman Sid Dinerstein sees him as a strong candidate. "He'll be a great person for the party. He's been throughout the state," Dinerstein said. "He has an infrastructure of contacts and fundraisers throughout the state."

Above, Lopez-Cantera greets supporters after announcing his candidacy for the Republican nomination for U.S. Senate in northwest Miami-Dade County on July 15, 2015.

U.S. Sen. Marco Rubio’s decision to seek the Republican presidential nomination instead of seeking re-election in 2016 created a rare political prize: an open seat with no incumbent. And that’s attracted a long list of high-profile Democratic and Republican candidates.

Rubio's seat is a toss-up that could be won by either party, national independent Senate analysts say.

All the candidates face a challenge that bedevils most people seeking statewide office in Florida and deters many from running.

The state is so big that even candidates who are well known in an important region like South Florida or Tampa Bay are usually virtual unknowns outside their home territory. Getting introduced to 4.2 million registered Republicans requires lots of money to advertise in the state's 10 media markets.

Many other Florida Democrats and Republicans have opted against running. For many, the chance at the ultimate prize – a seat in the Senate – isn’t worth taking since they’d have to give up sure bets at re-election to their current offices.